Replace allegro/bigcache with something lighter.

In high frequency environment the allegro bigcache caused significant
memory usage overhead. This commit replaces it with something much lighter.

utils/ordered_map/ordered_map.go

@@ -55,10 +55,67 @@ type customJsonEncoder struct {
 }
 
 func (e *customJsonEncoder) Encode(v interface{}) error {
-	data, err := json.Marshal(v)
+	if v == nil {
+		e.buf.WriteString("null")
+		return nil
+	}
+
+	switch val := v.(type) {
+	case *OrderedMap:
+		data, err := json.Marshal(val.values)
+		if err != nil {
+			return err
+		}
+		e.buf.Write(data)
+	default:
+		data, err := json.Marshal(val)
+		if err != nil {
+			return err
+		}
+		e.buf.Write(data)
+	}
+	return nil
+}
+
+func (o OrderedMap) Keys() []string {
+	return o.keys
+}
+
+func (o OrderedMap) Values() []interface{} {
+	var values []interface{}
+	for _, k := range o.keys {
+		values = append(values, o.values[k])
+	}
+	return values
+}
+
+func (o *OrderedMap) Delete(key string) {
+	delete(o.values, key)
+	for i, k := range o.keys {
+		if k == key {
+			o.keys = append(o.keys[:i], o.keys[i+1:]...)
+			break
+		}
+	}
+}
+
+func (o OrderedMap) Exists(key string) bool {
+	_, exists := o.values[key]
+	return exists
+}
+
+func (o *OrderedMap) UnmarshalJSON(data []byte) error {
+	var values map[string]interface{}
+	err := json.Unmarshal(data, &values)
 	if err != nil {
 		return err
 	}
-	e.buf.Write(data)
+
+	o.keys = []string{}
+	o.values = map[string]interface{}{}
+	for k, v := range values {
+		o.Set(k, v)
+	}
+
 	return nil
 }